McCaffrey, William D.¹, Ben Kneller² 
(1) University of Leeds, Leeds, United Kingdom 
(2) University of California, Santa Barbara, CA

ABSTRACT: Autocyclic vs. Allocyclic Controls on Aggradational Channel Progradation, Back Fill and Avulsion

Do characteristic changes in sedimentary architecture (either progressive or abrupt) arise naturally from the inherited geometry of a system and the type of flows traversing it, or do variations in the flows (random and/or cyclical) play a role in dictating changes in system style? Furthermore, if both auto- and allocyclic forcing mechanisms are in play, how do they interact? These questions apply to many different types of turbidite-dominated system. Here, we focus upon the controls on the development of aggradational submarine channels. These particular systems are interesting because their characteristic geometry necessarily causes both lateral and longitudinal sediment fractionation within the majority of turbidity currents that flow along them. We argue that the degree of this fractionation may progressively change during channel evolution, even if the inbound flows remain the same, necessitating changes in channel morphology that in turn may indirectly force avulsions. It can also be argued that such avulsion-inducing changes in channel morphology are produced by systematic (possibly cyclical) changes in flow type. We suggest that autocyclic controls may dominate during periods of high sediment input rate, with allocyclic controls being more significant when input rates are lower.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.